This invention relates to speech recognition apparatus and methods.
In complex equipment having multiple functions it can be useful to be able to control the equipment by spoken commands. This is also useful where the user's hands are occupied with other tasks or where the user is disabled and is unable to use his hands to operate conventional mechanical switches and controls.
The problem with equipment controlled by speech is that speech recognition can be unreliable, especially where the voice of the speaker is altered by environmental factors, such as vibration. This can lead to failure to operate or, worse still, to incorrect operation.
Various techniques are used for speech recognition. One technique involves the use of Markov models which are useful because they readily enable the boundaries between words in continuous speech to be identified. In noisy environments or where speech is degraded by stress on the speaker, Markov model techniques may not provide sufficiently reliable identification of the words spoken. Considerable effort has been made recently to improve the performance of such techniques by noise compensation, compensation, syntax selection and other methods.
An alternative technique which has been proposed for speech recognition employs neural nets. These neural net techniques are capable of identifying individual words to high accuracy even when speech is badly degraded. They are, however, not suited to the recognition of continuous speech because they are not capable of accurately identifying word boundaries.